Coupled radiation and conduction in a scattering composite layer with coatings

Transient coupled radiation and conduction in a two-layer isotropically scattering semitransparent nongray medium with thin opaque coatings is studied by the ray tracing method in combination with Hottel and Sarofim's zonal method and the control-volume method. The radiative energy transfer process in a semitransparent medium is divided into two subprocesses: without considering scattering and considering scattering. The radiative transfer coefficients of the composite are deduced under specular and diffuse reflection, respectively; internal multireflection, total reflection, and refraction are included. The method is extended to gain the radiative transfer coefficients of an isotropically scattering composite with combined specular and diffuse reflection. The radiative heat source term is calculated from the radiative transfer coefficients. The steady-state and transient temperature distributions and heat fluxes in the composite are obtained for the general boundary conditions of external radiation and convection. The present analysis includes the influences of emissivity, surface radiative properties, and spectral properties on the temperature distributions and the heat fluxes.